Windows 7 HP C7280 Double sided printing

For more detailis for others who have this problem (like I did) here's what HP's support told me to do to achieve the same thing in more steps than saltgrass and mazzaferro did.

Mr ____, I would like to inform that the two sided printing is not available in the windows 7 by default, so to print the two-sided (Duplexing) Printing under the Windows 7 you need to set the two-sided setting. I request you please click on the following link and perform the steps one by one:-

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NOTE: Please do not click on the link, please copy the link and paste it in address bar of the new Internet browser window and press Enter.

After the performing the steps provided in the above link , I request you please follow the steps given below to print.

1. On the Windows taskbar, click the Windows icon , type control printers in the Start Search box, and then press Enter . The Printers window opens.
2. Click Add a printer from the menu near the top of the window. The Add Printer dialog box appears.
3. Click Add a local printer . Click Use existing port: , make sure that USB001 or DOT4_001 is selected for the printer port, and then click Next .
4. Under Manufacturer , click HP , under Printers , click HP DeskJet 990c , and then click Next .
5. Click Use the driver that is currently installed , and then click Next .
6. Use the default printer name, click to remove the checkmark next to Set as the default printer , and then click Next .
7. Click Do not share this printer , and then click Next .
8. Click Finish to complete the setup.
9. Try to print any document and check the functionality.

Sounds like everyone who has a bidirectional duplexing printer will have this issue.